Inherent in most sports, and in many demanding workplace situations, is a distinct weight-bearing leg reaction movement sequence that must be quickly and accurately executed in response to the actions of an opponent, movement of a ball, or other visual cues and stimuli that cannot be predicted by the subject. When optimally executed, the reaction movement sequence will allow the individual to shift the body's center of gravity from its current position to a visually identified target or intercept position in the shortest possible time. As a result of injury, disease processes, musculoskeletal asymmetry or inappropriate training--the ability to initiate and coordinate weight-bearing movement may be compromised. Any dysfunction that affects muscular strength, power, endurance, coordination/agility, neurophysiologic function, musculoskeletal integrity or joint stability will affect movement to some degree.
In contrast to simple straight ahead running, a reaction movement sequence covers short distances--typically three to ten feet--and combinations of lateral, forward and backward movements. Athletic competitions are comprised of a multiplicity of movement sequences in response to the actions of an opponent, movement of a ball, or other visual cues and stimuli that cannot be predicted by the player. Few capabilities are more generic to athletics than quickness of movement to avoid or intercept an opponent or ball, generally short distance combinations of lateral, backward and forward motion, direction changes, and reaction movements. Undertaking the sequence requires perception and interpretation of a cue, decisions on optimal foot movement pattern and direction, and neuromuscular actuation response time and force output control to accelerate and decelerate body mass in any direction from the starting position. The reaction movement sequence may also require a quick change of direction towards a new intercept position, or stabilizing the body's center of gravity at the intercept position in order to best perform an action such as catching or throwing a baseball or executing a tennis backhand. Numerous examples of this react/shift/stabilize or react/shift/change direction movement sequence exist in almost all athletic activities involving a ball or team play and in many potentially injurious workplace situations.
Experts readily acknowledge that an athlete's capabilities to react, or any worker in physically demanding situations, and to accelerate and decelerate in any movement direction while maintaining appropriate balance and stability are among the most significant determinants of performance. Yet as critical as this reaction movement sequence is to successful play, and for on-the-job safety, heretofore there has not been available a system for measuring the individual components of a reaction movement sequence.
The quantifiable components of the reaction movement sequence may be defined as follows:
1. Reaction Time--The elapsed time from the appearance of a visual cue to a change in loading (force output to the ground) initiating the takeoff movement. This includes the time required to perceive the cue, interpret the required functional response in terms of direction and distance, and the neuromuscular activation time to initiate appropriate muscular contractions. Reaction time is not dependent on strength--the change in applied force that triggers reaction time measurement is very small. Unplanned movements may use different motor pathways and create different musculoskeletal stresses than pre-planned movements. Deficits in Reaction Time most likely result from one or a combination of the following factors: perception/interpretation problems that delay the movement decision; motor pathway dysfunction that affects neuromuscular activation time to initiate appropriate muscular contractions; pain, instability or other deterring sensation when a forceful movement is made in the deficit direction; lack of confidence in the capability of the injured limb that results in conscious or unconscious hesitation to move in the specified reaction direction.
2. Contraction Time or Ground Force Time--The elapsed time from initial change in loading until sufficient muscular force is generated to lift off initial weight-bearing position. This provides a means for reliably measuring the key component of functional muscular contraction time and for testing joint function during maximum effort takeoffs in different movement directions. Deficits in Ground Force Time most likely result from one or a combination of the following factors: instability, pain or other deterring sensations that prevent the subject from applying forces required to move quickly in the indicated direction; insufficient rehabilitation of equal strength and power in the involved extremity. The actual force during acceleration can also be quantified from the analog waveform.
3. Transit Time--The time from the instant of change in loading initiating the takeoff movement to full contact at the intercept position. Transit Speed is the distance traveled divided by time from the instant of force output initiating the takeoff movement to the instant of full contact at the target or intercept position. Transit time and thus transit speed is highly dependent on both muscular power acceleration and optimization of foot movement pattern for the direction and distance to be covered. Transit speed PG,5 is dependent on muscular power, but is even more affected by basic agility and optimization of foot movement pattern for the direction and distance to be covered. Improving transit speed is usually more a matter of practice and appropriate coaching than of specific rehabilitation programming.
4. Stabilization Time--The elapsed time from the instant of full contact at the target position to the moment that a stable stance is achieved, i.e., the time required for the individual to assume a stable stance after arriving at the target or intercept position. From the standpoint of sports performance, this measurement is designed to evaluate an athlete's ability to stabilize following rapid movement to an intercept position in order to best perform a task such as a catch and throw, tennis backhand or blocking maneuver. It is important to note that Stabilization Time is a new measurement construct that has had insufficient study to optimize threshold and window settings. However, it is expected to provide immediate value by allowing comparisons to be made using controlled, repeatable measurement criteria. Deficits in Stabilization Time likely result from one or a combination of the following factors: pain or instability in that compromises the subject's ability to decelerate body mass with the deficit limb insufficient rehabilitation of the plyometric/eccentric components of muscular performance; proprioception problems that result in prolonged stance or center of gravity corrections requiring muscular contractions that are measured as ground force changes; true balance problems that result in sway. Even small, low frequency forefoot to rearfoot or right to left weight shifting may result in ground force variations that are measured as longer ST's. The Stabilization Time measurement is not affected by bilateral weight distribution--its criteria are changes in ground force and time. This measurement uses threshold and window settings which can be adjusted by the clinician. The threshold setting is for magnitude of ground force variation (magnitude of oscillation or instability). The other setting is for duration of sample. The system measures how large the variations in force are over a specific time period or window. Measurement continues until no measured force variation greater than the threshold magnitude occurs in a single time window. Essentially, the system looks at stability over very small periods of time until the specified level of stability is maintained for an entire specified period. Stability Time measurement can be made less demanding (faster subsequent movement cues) by increasing the force variation threshold and shortening the time window.
5. Stabilization Index--The number of times ground force oscillations exceed a selected magnitude in a specified time period. Both the magnitude and duration "windows" are adjustable using the same utility as for Stabilization Time above. On landing from a vertical drop, or medial, lateral, forward or backward movement, the limb is required to absorb the impulse loads required to decelerate body mass which quickly decrease to stable weight-bearing load. During this period of loading change, the large initial spike in ground force is followed by a series of force variations (oscillations) which have a magnitude and frequency pattern that is affected by musculoskeletal factors. It is expected that a limb with "good" stability--i.e., intact and strong primary static restraints--will show a quite different magnitude and frequency pattern than a limb that is relying more on secondary, dynamic restraints to control joint integrity. If clinical trials bear out these expectations, an optimized stability index will provide a means for testing of functional stability and the documentation of surgical, rehabilitation and bracing treatments.
6. Ground Time--The time from instant of ground contact to the instant of takeoff. This is a key measure of plyometric/eccentric capability and is completely differentiated from Ground Force Time which is taken from a stable position on the platform. Plyometric performance capability is a reliable indicator of how efficiently the body uses the stored elastic energy of muscle and is also an indicator of neuromuscular efficiency in controlling muscle contraction. Ground Time allows quantification and comparison of one of the most important aspects of plyometric performance. Deficits in Ground Time will almost certainly result from any pain or instability, but otherwise are the result of insufficient plyometric/eccentric training.
7. Total Movement Time--The total time required to complete a specific programmed set or sequence of movements. This measurement appears in tests like the Single Leg Reaction/Stabilization Hop Test. This test can be performed with forward, medial, lateral or even backward hops. In the test for which Total Movement Time is reported, a number of other breakout measures such as best and average Ground Force Time may also be reported. Deficits in Total Movement Time may result from deficits in one or more of these individual factors. TMT is reported to give a composite or sum deficit which is expected to be a useful indicator of overall functional limitation in activities incorporating movements similar to the demands of the testing protocol. Individual deficits should be helpful in designing the rehabilitation protocol using concepts similar to those discussed above.
8. Jump Height--Height of vertical jump to within 1/2 inch. Maximum vertical jump is an excellent indicator of peak muscular power output and correlates well to overall athletic performance capability for many sports. Vertical jump height can be tested in many ways, but only a force platform can measure how quickly an athlete reacts and gets off the ground. The force/time transducer platform quantifies the following factors; Jump Height; Reaction Time; Takeoff Time, the time from instant of vertical jump cue to instant of takeoff; Total Jump Time from jump cue to takeoff (overall, a quicker takeoff is often more important than jump height). The duration of the eccentric and concentric phases of jump or horizontal acceleration can also be quantified.
When measuring transit rates over short distances, two critical components comprise the elapsed time from visual cue to arrival at the intercept position; the reaction time, and the transit time. The reaction time can be a significant portion of the total elapsed time. For example, the reaction time will typically vary between 0.2 to 0.4 seconds, and the transit time, predicated on the distance and direction traveled can vary from 0.5 to more than a second. Therefore, without the ability to accurately and reproducibly measure reaction time and separate it from the total elapsed time, the coach, trainer or clinician would be unable to determine the real transit time, and thus, discern the source of any deficiency.
Additionally, reaction time can be an important parameter to consider when evaluating an athlete's recovery from any injury. For example, though an athlete may have recovered physically from an injury, he may not have yet regained the confidence to explode off the injured limb. Any hesitation would be reflected in increased or longer reaction times.
In any one individual, as a result of injury, musculoskeletal asymmetry or inappropriate training, the ability to initiate and complete a reaction movement sequence may vary depending on the required movement direction. Comparing the specific movement vectors between the left and the right can quantify any deficits such that appropriate rehabilitation and/or training programs can be developed, progressed and monitored for effectiveness. For orthopedic rehabilitation applications, it is particularly important that the system allow reaction movement challenges to be controlled in both timing and distance to stay within prescribed limits of musculoskeletal stress.
For the testing method to be valid, objective and meaningful, the complete reaction movement sequence requires visual movement cues that appear in a realistic spatial representation and that clearly specify the required functional response. It is essential that the timing of each visual movement cue and/or the functional response specified be unpredictable to the individual being tested. Also the movement area must be of sufficient size to allow replication of relevant movements.
Certain critical moments within the reaction movement sequence cannot be discerned visually. Accurate measurement of the individual components of the reaction movement sequence requires a system capable of detecting minute loading changes in the movement area.
Another requirement for accuracy is the capability to reliably locate a subject's body center of gravity in order to measure movement distances and calculate movement speed. Previous technologies rely simply on detecting any contact with a target position. Merely contacting a position cannot be interpreted as effective movement of full body mass to that position. In the measurement of short distance movements, in particular, the error inherent in this method becomes so great that it may not be possible to distinguish reliably between world class and average performances. Furthermore, this method allows a subject, particularly one with long limbs, to cheat the test. To address this problem, means must be provided to insure that the subject starts and finishes at known points, i.e. that his center of gravity is accurately and consistently located at the beginning point and ending point of each movement. This invention accomplishes this requirement by requiring bilateral foot contact on two spaced positions that confine the distance variable yet still allow an appropriate functional response.
Various approaches have been suggested for assessing athletic movement and performance. None, however, have addressed and fulfilled the requirements for validly, objectively and meaningfully testing the complete reaction movement sequence. Elstein et. al. U.S. Pat. No. 4,702,475 discloses a rectangular exercise mat having marked pressure sensitive response areas around the perimeter. In response to a light prompt, the participant moves to a new response area thereby executing a directed movement pattern. The response areas are coupled to pressure sensitive binary switches. The system measures the time period from the prompt to the touching of the designated response area thereby activating the switch. The system does not measure reaction time from the appearance of the prompt to the beginning of change in loading that initiates the takeoff movement. Nor does the system measure contraction time from initial change in loading to lift off or the transit time from change in loading to full contact at the response area. Further, it does not measure the stabilization time from contact at the response area until a stable stance is achieved.
Yang U.S. Pat. No. 4,627,620 discloses an apparatus for measuring reflex, speed and accuracy wherein multiple targets are spread around the participant. The targets are prompted acoustically or visually and directing the participant move to and manually strike the target. A timer is activated at the prompt and deactivated at the strike by a binary switch. The time interval between the prompt and the strike is measured and displayed. The system does not and cannot measure reaction time, contraction time, transit time or stabilization time as described above.
Williams U.S. Pat. No. 4,645,458 discloses a training system wherein a player responds to a light prompt to leave a starting point and go to a first reaction point. The player is timed over the distance. At the first reaction point, a second light prompt directs the player to a second reaction point. The player is timed from the starting point to the second reaction point. As in the aforementioned prior approaches, the system does not measure reaction time, contraction time, transit time or stabilization time.
Alton U.S. Pat. No. 3,024,020 discloses an apparatus for testing agility wherein a floor platform has a geometric pattern of foot activated switches. A light display includes lamps arranged in a pattern similar to the floor platform. A selector box activates the lights to indicate a subsequent foot placement for the player. When the player attains that placement the lights are extinguished and another light set activated. The pace can be manually or automatically controlled through a predetermined movement path. The apparatus, while providing a sequenced movement path does not provide reaction time, contraction time, transit time or stabilization time.
Bigelow U.S. Pat. No. 4,534,557 discloses a reaction time and applied force feedback training system wherein a stimulus indicator, associated with a plurality of training devices, is energized to provide a signal to which the player responds by striking the training device. The system displays the time from the stimulus to the striking and the magnitude of the applied force. The system does not provide reaction time, contraction time, transit time or stabilization time.
Various video game formats have used a playing platform containing an array or pressure actuated switches. In response to character dramatization on a video screen, the player alters foot movement pace or changes direction in accordance with game rules. As in the aforementioned approaches, the binary switching does not fulfill the requirements for reaction movement sequence measurement.
In view of the foregoing limitations, it will be appreciated that the prior approaches, while providing stimulus prompted movement and indicia of performance, do not provide systems for testing and training of the important parameters of reaction movement sequence allowing assessing of performance and progress for relevant training and rehabilitation movements.